My invention relates to a circuit for controlling a radio receiver, and particularly to such a circuit that provides such control in response to several conditions in the radio receiver.
Modern radio receivers are provided with a number of functions to make the receivers more versatile or more useful. For example, a frequency modulation (FM) receiver is provided with a noise squelch circuit which squelches (or blocks the audio of) the reciever until a radio frequency carrier is received so as to keep the user from having to listen to spectrum noise in the absence of received carrier signals. Radio receivers can be provided with a channel guard circuit which blocks the audio until a tone of proper audio frequency is received so that the user does not have to listen to communications intended for other users. Similarly, radio receivers can be provided with a paging circuit which produces a paging signal to alert the user that he is being paged. There are situations where a user may wish to change his receiver from responding to one type of circuit, such as a channel guard circuit, to another type of circuit, such as a paging circuit.
Accordingly, a primary object of my invention is to provide a new and improved circuit for controlling the response conditions of a radio receiver.
Another object of my invention is to provide a new and improved circuit for causing a radio receiver to change its response from one condition or set of conditions to another condition or set of conditions.
Another fairly specific object of my invention is to provide a new and improved circuit for causing a radio receiver to be responsive to a radio frequency carrier and a channel guard signal; or to a radio frequency carrier and a paging signal; or to a radio frequency carrier, a channel guard signal, and a paging signal.
At times, the operability of the radio receiver may have to be checked. Accordingly, another object of my invention is to provide a new and improved circuit for controlling the response conditions of a radio receiver and for checking the operation of the receiver as well.
Previously, changing the control conditions of a radio receiver such as described above required the use of jumpers or wiring changes. Accordingly, another object of my invention is to provide a new and improved circuit for controlling the response conditions of a radio receiver, the response conditions of the control circuit being easily and quickly changed.
When a radio receiver such as described above becomes inoperable for some reason, locating the fault has been a difficult and time consuming job.
Accordingly, another object of my invention is to provide a new and improved circuit that controls the response conditions of a radio receiver, and that can be easily and quickly checked for faults or failures.
Another object of my invention is to provide a new and improved control circuit having condition response circuits that removably engage respective receptacles which produce the proper condition signal to the control circuit upon removal of the condition response circuit, thereby indicating whether the removed condition response circuit was functioning properly.